This invention relates to a process for the recovery of metal values from complex sulfide concentrates and, more particularly, relates to a process for hydrometallurgically treating lead sulfide concentrates for the recovery of lead and other non-ferrous and precious metal values.
Complex sulfide concentrates which may contain lead, zinc, iron, arsenic, antimony, bismuth, copper, silver, gold and the like values have historically been treated in pyrometallurgical processes. Hydrometallurgical processes normally have not been able to cope with such complex compositions either technically or economically. However, rapidly increasing metal prices, higher hygiene standards established for pyrometallurgical processing, and advances in technology have made hydrometallurgical processing of complex sulfide-containing concentrates more attractive.
A number of routes for the hydrometallurgical processing of complex lead sulfide-containing concentrates have been considered, but most have been proved to be either unsuitable for obtaining economical yields of metal values to be recovered or were burdened with prohibitively high costs. Such routes include sulfuric acid pressure leach systems, followed by amine or ammonia extraction, and chloride-based leach systems.
Known prior art on processes using chloride-based systems for the hydrometallurgical processing of lead sulfide-containing concentrates usually disclose a leach wherein an aqueous lixiviant is used which may contain one or more compounds of the group consisting of ferric-, ferrous-, sodium-, magnesium- and calcium-chloride and which may be acidified with either hydrochloric or sulfuric acid. The leach usually is performed hot at atmospheric pressure, lead chloride formed may then be crystallized and subjected to electrolysis for recovery of lead, and the lixiviant recovered and/or regenerated and recycled to the leach.
Typical of these processes are those patented by Niels C. Christensen during the period of 1920 to 1930. For example, according to U.S. Pat. No. 1,435,891, which issued on Nov. 14, 1922, lead-zinc sulfide ore is leached with hot ferric chloride, lead is preferentially dissolved, silver is precipitated and the solution is electrolyzed or cooled and the lead chloride crystallized, melted and electrolyzed. The ferric chloride is regenerated by absorbing chlorine in the residual ferrous chloride solution. The leach residue is treated with sulfuric acid. According to U.S. Pat. No. 1,441,063, which issued Jan. 2, 1923, lead, silver and copper sulfides are leached with a hot chloride lixiviant which comprises sodium-, calcium-, magnesium- or ferrous-chloride as well as ferric-chloride and some hydrochloric acid; silver and copper are cemented from the leach solution and lead is precipitated by electrolysis from aqueous solution or from fused lead chloride. The lixiviant does not act upon pyrite, chalcopyrite and some complex arsenical silver compounds, but does act upon zinc blende to a limited extent.
More recently, a similar process has been disclosed in U.S. Pat. No. 3,929,597, which issued on Dec. 30, 1975. According to this process, lead and silver are produced from sulfides containing lead, silver, zinc and iron by leaching with a ferric salt solution, at 25.degree. - 100.degree. C., separating leach solution from leach residue, leaching the residue with a sodium chloride brine, at 50.degree. - 100.degree. C., cooling the resulting solution to crystallize and separate lead salts, cementing silver from the remaining solution and producing lead by molten lead salt electrolysis. The ferric salt solution is regenerated by contacting the leach solution which contains ferrous salt with chlorine evolved in the electrolysis. A portion of the leach solution is bled off. The residue from the brine leach is treated in a sodium sulfide leach resulting in a sulfide bleed stream and solids, which are treated in a second ferric leach followed by a brine leach for further dissolution of values. A final residue from these second leaches is removed from the process.
Prior art processes, including the processes of the foregoing references, have several limitations. They do not disclose techniques for the separate and economical recovery of metal values contained in complex sulfides, for treating process effluents for the recovery of values in such a manner that pollution is obviated, or for possible integration in a metallurgical plant wherein complex lead containing sulfide concentrates are treated separately from other concentrates. Moreover, the prior art does not disclose techniques and conditions for more selective separation of values in leaching or for careful control of the water mass-balance in the process to enable economic operation.